Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
831~
BLADDER DEVICE FOR DISPLACING 53,739
AIR IN BOT~LE BOR~ SHAFq'
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This application is related to U.S. Patent 4,699,008
entitled APPARATUS FOR ULTRASONICALLY INSPECTING A LARGE SHAFT
FROM A LIQUID-FILLED BORE, U.S. Patent 4,670,029 entitled
WATER TREATNENT SYSTEM FOR ULTRASONIC INSPECTION OF TURBINE
ROTORS FRON THE BORE and U.S. Patent 4,803,638 entitled
ULTRASONIC SIGNAL PROCESSING SYSTEM INCLUDING A FLAW ~ATE,
assigned to Westinghouse.
This application is also related to copending Cana~ian
applications entitled BORESONIC INSPECTION SYSTEM and bearing
application No. 540,5&9 and BORE MAPPIN& AND SURFACE TIME
MEASUREMENT SYSTE~ bearing application No. 539,740.
BACRGROUND OF TH~ INVENTION
Field of the Invention
The present invention is directed to an apparatu~ for
removing air trapped in a bottle bore of a shaft and, more
particularly, includes an expandable bladder which displaces
the trapped air and allows it travel up the tilted shaft.
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Descrlption of the Rel _ed Art
The present invention i8 used with an
ultrasonic inspection system for inspecting the bore o~
a turbine or generator rotor shaft. Such an inspection
system is described in detail in the aforementioned U.S.
patents and Canadian applications. Such rotors
~~~~are very làrge and may be as m~ch as 45 feet in
length and several feet in diameter. It is
common practice to bore out the center of the
shaft to remove flaws in the rotor material.
Even after the center of the shaf~ has been
removed, flaws in the steel material near the
bore surface may still exist and routine
inspec~ions are necessary to determine whether
the flaws have expanded due to operating stress
and to ensure that the shaft ls safe from
catastrophic ~ailure.
Immersion type ultrasonic i~spection,
as practi~ed in the above-identified U.S. patent
applications, requires the use of a liquid such
as water as a coupling medium for transmitting
ultrasonic pulses from the transducer into the
rotor material. Flaws are detected based on
reflectlons of the ultrasonic sound wave from
material discontinuities.
A bottle bore shaft is a shaft in
which the mid portion has a larger diameter ~han
the exterior por~ions. Air can be trapped in
the bottle bore portion of the shaft even when
the shaft is tilted from a horizontal position.
Trapped air reflects and/or diffuses the
ultrasonic pulses and ~he pulse path cannot be
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reliably determined. Trapped air can prevent
the inspection of the portion of the shaft where
the air is trapped. For a complete inspection
the air must be removed from the shaft.
S one method which removes most of the
air is described in U.S. patent
4,670,029 and involves the application of a vacuum
to the water fiiled shaft. Because a perfect
vacuum cannot be achieved in the presence of
water, about a tenth of the aix initially
trapped in the bottle bore will remain to form a
much smaller air pocket producing a bubble which
blocks inspection. Figure 1 illustrates how a
bottle bore 8 can trap air 10 in a water filled
12 shaft 14 even when the shaft 14 is tilted and
a vacuum dearation system is used to remove as
much air as possible.
Another method uses a long small
diameter flexible tube at the end of a sensing
head to suck the ~rapped air from the bottle
bore. The tubc must be attached to a
manipula~or normally used to position a
transducer. This sy~tem depend~ on precise
pasitioning of the tube at the highest point of
2S the surface pred1cted to harbor the bubble and,
since a person cannot actually observe that all
the alr has been removed, this method does not
assure complete remov~l.
Another much lesæ expensive method
uses a flexible vinyl (TYGON) tube attached to
the end of a plumbers snake. A small plastic
float is attached to the end of a short length
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of the tube which extends beyond the snake. The
snake inserts the tube into the bottle bore
where the float lifts the tube into the air
pocket where the air is removed by suction.
This device is difficult to control and does not
assure complete air removal.
SUMMA~Y OF TEE I~V~NTION
It is an object of the present
invention to remove substantially all air
trapped in a bottle bore of a turbine or
generator shaft.
It is another object of the present
invention to provide a simple low cost trapped
air removal system.
It is an additional object of the
present invention to provide an air removal
system that does not re~uire precise placement
of the air removal device.
It is a further object of the present
invention to provi~e an air removal system that
provides the user with a high confidence level
that all trapped air has been removed.
The present lnvention incIudes a
complia~t air filled bladder and a device for
inserting the bladder into the bottle bore
region o~ a large turbine or generator sha~t.
The flexible bladder floats to the ~op of the
bottle bore and displaces the air trapped in the
bottle bore region by conforming to the interior
surface of the bottle bore. The bladder forces
the air down to a position where it will escape
to the upper end of the shaft along the slightly
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tilted interior surface of the shaft. An outer
insertion tube is provided for protecting the
rather fragile bladder during insertion. The
- bladder can be inflated by pumping pressurized
gas through an inner tube into the bladder. The
bladder can also be inflated by sealing a small
amount of air in the bladder and inner tube, and
then applying a vacuum to the turbine shaft
during a vacuum dearation air removal procedure,
These together with other objects and
advantages which will be subsequently apparent,
reside in the details of construction and
operation as more fully hereinafter described
and claimed, reference being had to the
accompanying drawings forming a part hereof,
wherei.n like numerals refer to like parts
throughout.
BRIEF D~SCRIPTION OF TH~ DRAWI~GS
Figure l illustrates how air can be
trapped in a rotor shaft ~4 even when a vacuum
is applied thereto;
Figures 2 and 3 illustrate how a
compliant bladder 30 will displace air trapped
in a bottle bore 8; and
Figure 4 illustrates one method of
coupling the bladder 30 to an air p~mp 42.
D~SCRIPTI~N OF T~F PRERER~D RMBODI~NT
The present invention, as depicted in
Figures 2 and 3, is an inflatible, compliant
bladder 30 attached to a small tuba 32 which is
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used to inflate the bladder 30 while in the
bottle bore 8. The bladder 30 is a very
compliant substance, such as for example, latex
rubber, silicone rubber, polyvinyl or
polyethylene film, which will allow the bladder
to substantially conform to the interior shape
of the bottle bore 8 so that substantially all
the air trapped in the bottle bore will be
displàced. The small inner tube 32 is made of
plastic such as polyethylene or polyvinyl. This
tube 32 must be sufficiently stiff to be able to
push the bladder 30 out o~ the larger outer tube
34 and to also retract the collapsed bladder 30
back into the tube 34, while at the same time
- 15 being flexible enough to allow the bladder 30 to
float to the top of the bottle bore 8. The tube
32 could have a flexible end piece and a rather
stiff shaft to allow this dual function to be
performed at low cost.
The larger outer tube 34 acts as a
protective cover and a stiffening device for
insertion o~ the bladder 30 and should have a
length sufficient to reach the battle bore
portion 8 o~ the shaft 14. A PVC pipe will
provide an acceptable light weight outer tube
34.
The bladder 30 is inflated through
tube 32 and holes 35 which are positioned inside
bladder 30. The bladder 30 is sealed at both
ends 38a and 38b to the tube 32 and the tube 32
is also sealed at the ~ar end 38a. The bladder
30 is used most effeatively with the vacuum
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dearation method described in U.S. patent 4,670,029.
However, the bladder 30 produces ade~uate air
displacement in the bottle bore 8 when used at
atmospheric pressure. It is also possible to
in~late the bladder 30 with a light gas such as
helium.
When used with the preferred vacuum
dearation method, the bladder 30 is inserted in
a collapsed condition into the shaft 14 through
an adapter 16 which is completely unde~water in
a water filled tank 40 as illustrated in Figure
4. The bladder 30 is positioned in the
protective tube 34 in a collapsed condition.
When the tube 34 has the bladder 30 in the
appropriate position the protective tube 34 is
retracted to expose the full length of the
bladder 30 and a sufficient portion of tube 32
to allow the bladder 30 to float freely when
expanded. To properly position the tube 34 in
the shaft 14, the tube 34 should be marked with
distance measuring graduations so that insertion
to the proper position is possible~ Once the
bladder 30 ls in po8it~ on, a pump 42 can be used
to inflate the bladder 30. It is also possible
to seal the inner tube 32 at the auter end 44.
If the tube 32 is sealed at the outer end 44, it
should contain sufficient air to inflate the
bladder to an absolute pressure of about 5
inches of mercury when the external pressure in
the bore is reduced to about 3 inches o~
mercury. Since the water 12 filling the bore is
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at law pressure the inflated bladder 30 will
float and displace the air at the tap of the
bottle ~ore 8 to cause the air outside the
bladder 30 to migrate down to the main level of
the bore where it can escape up the tilted shaft
14 and be evacuated from the upper end.
It is also possible to position the
bladder 30 at the farthest end of the shaft 14
and slowly pull it out allowing it to float
along the upper surface of the shaft bore. This
method is not preferred because it complicates
the seali~g problem when a vacuum is applied to
the shaft 14 but`may be adequate without
applying a vacu~m to the shaft 14.
Since the bladder 30 is made from a
very elastic and compliant material it will
displace substan~ially all of the air. If the
vacuum dearation method is used, when the bore 8
is returned to atmospheric pressure any very
small bubbles which remain will contract to
l/lOth of their initial size so that the few
tiny remaining bubbles will not adversely affect
any ultrasonic inspection. In the vacuum
d~aration method, as the bore 8 returns to
atmospheric pressure and if the sealed end type
tube 32 is used, the bladder 30 will contract to
its fully collapsed condition so the protective
tube 34 can be extended over the bladder 30 and
withdrawn without causing damage.
If additional air needs to be removed
from the bottle bore 8 the sealed end of the
tube 32 can be exposed to atmospheric pressure
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and the bouyancy of the bladder 30 will be
substantially increased thereby further
displacing trapped air. It is also possible to
produce a positive gas pressure in the bladder
30 by using a pump 42. However, in this method
the pressure applied to the bladder 30 should
not be excessive since the bladder 30 would
rupture. In this method it is also better not
to fully inflate the bladder so that it will be
more compliant.
If the sealed tube method is used, the
amount of air reguired inside the tube 32 and
the bladder 30 can be calculated and permanently
sealed therein, since the volume of air required
can be determined by the approximate ratio of
the pressures and the final required volume is
approximately constant. If the air pump method
is used an absolute pressure o~ abou~ 5 inches
of mercury in the bladder 30 would be
appropriate. .
When the present invention is used at
atmospheric pressure it should be used after
vacuum dearation because it is best to evacuate
the bore and remove all air clissolved in the
water so that when the invention is inserted and
used to remove the trapped air, additional
dissolved air will not later rise to the top of
the bottle bore 8. In this method the inner
tube 32 must be inflated at a pressure of abaut
3 inches of mercury above atmospheric pressure
to displace the air in the bottle bore 8.
It is also possible to inflate the
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bladder 30 so that it completely fills the shaft
at tha location of the bottle bore 8. This
approach is not recommended because it could
prevent the air from migrating up the bore to
escape. In addition the bladder 30 thickness
would have to be so great that it may not fully
conform to the shape of the bottle bore 8, thus
allowing trapped air to remain.
The many features and advantages of
the present invention are apparent from the
detailed specification and thus it is intended
by the appended claims to cover all such
features and advantages of the invention which
fall within the true spirit and scope.thereof.
Furthermore, since numerous modifications and
changes will readily occur to those skilled in
the art, it is not desixed to limit the
invention to the exact construction and
operation illustrated and described, and
accordingly, all suitable modifications and
equivalents may be resorted to, falling within
the scope of the invention.
What is Claimed is:
